The current invention relates to the field of the identification of individuals using biometrics, and, in particular to the method of using a scan of the iris of the eye of the individual to make a positive identification.
An iris recognition system consisting of a CCD, or CMOS type sensor and an illumination system work together to provide an iris image of sufficient exposure and detail to obtain the critical iris texture required for a positive identification of an individual. Common illumination techniques for typical CCD or CMOS sensors use light in the visible and infrared wavelengths.
A problem arises when utilizing this system to identify individuals wearing eyeglasses. To illuminate the individual""s iris, narrow (spot) light beams are preferred. These illuminators cause reflections in the glasses of the individual, thereby occluding portions of the iris needed for iris recognition. These occlusions, called specularities, occur when the spot light beams reflect off of each surface of the lens of the individual""s glasses, that is, the surface encountered when the light enters the lens and the second surface encountered when the when the light leaves the lens. Thus, for each spot light source, there will be a pair of specularities visible from the perspective of the sensor. A similar problem can occur when one seeks to take an image or see a product contained in a transparent container, such as a glass jar or a blister package.
This problem can be addressed by adopting a dipole configuration of illuminators, with one illuminator being offset to the right of the sensor and one illuminator being offset to the left of the sensor. This configuration does not eliminate the specularities, but moves them away from the iris. As the angle from each illuminator to the sensor widens, the specularity will move away from the center of the image as seen by the sensor, such that the important areas of the iris or other object of interest are no longer occluded. Two illuminators are required to offset a gradient of illumination as seen by the sensor because the source of the light is moved to the side.
There are, however, disadvantages to this solution. First, two illuminators are required as opposed to just one, increasing production costs and requiring more power to operate. Second, the pair of illuminators must be spaced far enough apart such that the specularities introduced by each illuminator is far enough offset from the center of the images as seen by the sensor so as to not occlude important parts of the iris. This requires a larger housing than would otherwise be necessary, and as a result, a larger footprint for the overall unit.
Therefore, it is desirable that a single illuminator in a monopole configuration be utilized to illuminate the individual""s iris, or the object contained within a transparent container, thereby reducing the number of specularities. It is also desirable to minimize the effects of the specularities that are introduced by the illuminator by making the specularities smaller in size, while still supplying enough light energy on the object to support the image sensor aperture and depth of field requirements.
The invention consists of a micro-lens which, when fitted to the appropriate illuminator, will focus the beam of light on the iris and at the same time block a portion of the light emitted. The design goal is to reduce the size of the specularity such that, even though a portion of the iris may be occluded, the amount of information that is missing is statistically insignificant, to the point that a positive identification can still be made.
In the preferred embodiment, the illuminator is a commercially available light emitting diode (LED). Preferably, the LED will have a pair of dies, one die emitting infrared light having a wavelength of approximately 880 nm, and one die emitting visible light having a wavelength of approximately 730 nm. A single die configuration may also be used, as may illuminators which are not light emitting diodes.
Preferably, the illuminator with the micro lens will be placed very near the sensor, in a monopole configuration. In such a configuration, any tilting of the head of the individual offaxis from the sensor will move the specularity out of the way of the iris, as opposed to the dipole configuration, in which a tilting of the head would move one pair of specularities away from the iris, but would also move the other pair of specularities toward the iris.
To focus the emitted light, the micro-lens is designed so that when coupled to the LED, the emitted light view angle is reduced and the projected area is reduced. The light view angle, or field of view (FOV) is controlled by the lens focal length. A longer focal length focuses more light on the target eye as compared to the stand-alone LED.
The aperture of the micro-lens determines the incident specularity size. Consequently, a reduction in lens aperture will reduce the incident specularity size. The micro-lens has an aperture no larger than the die pair in a dual-configuration LED, and no larger than a single die in a single configuration LED. The result is an illuminator that generates smaller spectral reflections on the eyeglasses, while still adequately illuminating the iris.
The micro-lens will also block a portion of the emitted light. The total light emitted, in the case of an LED, has a component that is emitted directly from the die and a component that is reflected off of the substrate to which the die(s) is bonded. In many cases, the substrate is gold. The goal is to eliminate or to reduce as much as possible the light which is being reflected off of the substrate, leaving only the light which is emitted directly from the die. This provides the minimum sized specularity for the maximum amount of emitted light.
The masking of the reflected portion of the light is accomplished by way of an opaque material which surrounds the focusing portion of the micro-lens. The opaque material would be donut-shaped, with the hole containing the focusing portion of the lens just big enough to allow all light from the die to project. This configuration is unable to eliminate all of the reflected light because the hole is circular, and the dies are usually rectangular in shape. Additionally, in the case of a dual-die configuration, light reflected from the portion of the substrate in between the dies will be allowed to project. In both cases, however, the reflected light which projects due to the geometry of the lens is a small percentage of the entire light and does not add much to the size of the specularities.